1. Technical Field of the Invention
The invention concerns a manually controlled installation for spraying coating product, meaning an installation employing a manually controlled pneumatic sprayer including a trigger controlling both the flowrate of the coating product (paint) and the degree to which the valve controlling the input of air to spray this product is open.
The invention is more particularly directed to improvements to secure better control of the flowrates of air and coating product. It finds a particularly advantageous application in installations employing two-component paints or varnishes (typically a base and a hardener) whereby the volumetric ratio between the two-components is better controlled under all circumstances.
2. Description of the Prior Art
A conventional manually controlled paint spraying installation comprises at least one pneumatic sprayer including a trigger and connected to a paint feed line and to a compressed air feed line. The paint is "atomized" and propelled by the air towards the object to be painted. The user controls the jet of sprayed paint by pressing the trigger to a greater or lesser extent. The paint passes through a valve controlled by the trigger. The valve exercises a proportional action, meaning that it is arranged in such a way that the flowrate of the valve is a function of the degree to which the trigger is depressed. The air feed control valve, also controlled by the trigger, is of the "on-off" type, however; this means that the air flowrate remains virtually constant whatever the paint flowrate. It has been found that this particular feature of known sprayers can in itself be prejudicial to good spraying. It can be deleterious to use too much air for a relatively low paint flowrate. It has been found that the excess air tends to dry the paint before it reaches the object to be painted, which can result in a bad finish. One object of the invention is to resolve this problem.